Conventionally, a vehicle presence notification apparatus that notifies of presence of a vehicle is employed, especially, in a silent vehicle, such as an electric vehicle, a fuel cell vehicle, and a hybrid vehicle. The vehicle presence notification apparatus includes a speaker that generates a notification sound to outside the vehicle. A volume of the notification sound is set so that the notification sound can notify the surrounding area of presence of the vehicle while taking into consideration vehicle noise. In other words, the volume of the notification sound is smaller than a warning sound generated by a vehicle horn.
Thus, in the interior of the vehicle having a high sound insulation, it is difficult to hear the notification sound generated to outside the vehicle. Even in a state where a window is open and outside sound enters the interior of the vehicle, it is difficult to hear the notification sound in the interior of the vehicle due to load noise. In this state, even if a disconnection of the speaker is caused by some kind of failure and the notification sound is not emitted to outside, a user may not notice the absence of the notification sound and the vehicle may run without the notification sound.
Although it is not mounted in a vehicle, JP-A-2003-274491 discloses disconnection detection means for detecting disconnection of a speaker.
The disconnection detection means detects the presence or absence of disconnection of a speaker circuit in a broadcasting facility. The disconnection detection means includes (a) a speaker circuit coupled with a speaker for broadcasting, (b) an equivalent circuit having the same impedance with the speaker circuit, and (c) a disconnection detection circuit that determines the presence or absence of disconnection of the speaker circuit based on a difference between a voltage at a time when the speaker circuit is driven by an alternating current signal and a voltage at a time when the equivalent current is driven by the alternating current signal.
Thus, the disconnection detection means disclosed in JP-A-2003-274491 needs a switching circuit that switches between the speaker circuit and the equivalent circuit and the equivalent circuit using a dummy resistor having the same impedance with the speaker.
The dummy resistor is a resistor that needs a high breakdown voltage for exchanging energy generated by the speaker to heat when the dummy resistor is switched from the speaker and is driven by the alternating current. Even through the dummy resistor is used only at a disconnection detection, the dummy resistor is generally large, heavy, and expensive. Thus, it is undesirable to mount the dummy resistor in the vehicle. Specifically, if a disconnection of the speaker of the vehicle presence notification device is detected using the technique disclosed in JP-A-2003-274491, a size, a weight, and a cost of the vehicle present notification device may be increased.